In general, a network device performs a communication by sending a signal such as a packet destined to a destination identifier that represents the destination, such as IP address. When one destination identifier is renamed among a plurality of devices connected to a network, a signal that is supposed to be sent to a given device is sent to another device. Thus, it is possible for a sender to change a destination device without changing the destination identifier. The technique for realizing this is hereinafter referred to as destination switching technique.
Further, as a technique to continue processing even when failures occur in a network device such as a router, there is available a redundancy technique that uses a redundancy protocol such as Virtual Router Redundancy Protocol (VRRP), HSRP (Hot Standby Router Protocol), or ESRP (Extreme Standby Router Protocol) which are specified in RFC2338.
In this technique, a plurality of devices having the same level capability are previously prepared, in which one device is set in an operating state and the other device in a standby state. When the device being in an operating state fails to operate for any reason such as failures, the device being in a standby state detects that and automatically switches its own state from standby-state to operating state. As a result, operation continuity can be secured.
Generally, in a redundancy protocol such as VRRP, a signal called “heartbeat” is periodically (every one second, in the default setting of VRRP) sent from a device in an operating state to a device in a standby state to notify that the device in an operating state performs normal operation. The device in a standby state always waits for the heartbeat to be sent from the device in an operating state. When the interval between the heartbeats becomes longer than a predetermined threshold, the device in a standby state determines that the device in an operating state cannot perform normal operation and switches its own state from standby state to operating state.
Simultaneously with the switching between the device in an operating state and device in a standby state, a switching of authority to receive a signal destined to a destination identifier, which is shared among the devices in a redundant configuration, is made among the devices. This configuration realizes the switching of devices to perform processing while maintaining a state where a user always connects to the same virtual destination identifier.
Techniques related to the present invention will be described. Patent Document 1 discloses a technique that monitors a state of WAN (Wide Area Network) using a network monitoring unit and issues a VRRP packet of priority of when failures occur to switch a MASTER device. In this technique, although the switching of a MASTER device is made intentionally by an external instruction, the switching is also made automatically when failures occur in a router itself. Further, in this technique, a function executed at the time of failures is newly added to the VRRP, so that it is necessary to modify the router configuration.
Patent Document 2 discloses that a technique such as a remote mirror is used to enable issuance of the heartbeat through a path different from normally used to thereby realize the redundant configuration of the heartbeat. Patent Document 3 discloses a technique that includes a redundancy alternative port for a communication among a plurality of routers and transfers an advertisement packet on a path through the redundancy alternative port at the time of disconnection fault of a line connected to a router. Patent Document 4 discloses a technique that continues issuing an alarm signal using a pseudo alarm unit to a system that automatically shifts to a standby mode in the time zone when there is no alarm to thereby maintain a normal mode even after an actual alarm has been stopped.
Patent Document 1: Jpn. Pat. Appln. Laid-Open Publication No. 2003-258843
Patent Document 2: Jpn. Pat. Appln. Laid-Open Publication No. 2002-312189
Patent Document 3: Jpn. Pat. Appln. Laid-Open Publication No. 2003-051835
Patent Document 4: Jpn. Pat. Appln. Laid-Open Publication No. 10-214391